Conventionally, in a wireless communication to transmit and receive digital data, there has been known a phase modulation method, such as binary phase shift keying (BPSK) modulation or quadrature phase shift keying (QPSK) modulation, as a modulation method. In, for example, Institute of Electrical and Electronic Engineers (IEEE) 802.15.4 which is known as wireless network standards for a relatively short range, the BPSK modulation or the QPSK modulation is used as a modulation system.
Meanwhile, frequency shift keying modulation (hereinafter, also referred to as FSK modulation) is frequently used.
When the phase modulation is compared to the frequency modulation under the same wireless communication path conditions, it is known that the phase modulation (the BPSK modulation or the QPSK modulation) can generally communicate over relatively long distance but has a feature that the envelope of the transmission signal is not constant. As the example illustrated in FIG. 1, the value of the output envelope of the BPSK modulation largely fluctuates together with the modulation data. When the envelope fluctuates in this manner, a final stage amplifier circuit of a transmitter is complicated, and the power consumption can be increased.
Thus, there has been proposed BPSK modulation with a constant envelope (for example, see Non Patent Document 1).